title: Nonlinear dependence between the surface reflectance and the duty-cycle of semiconductor nanorod array.
abstract: The nonlinear dependence between the duty-cycle of semiconductor nanorod array and its surface reflectance minimization is demonstrated. The duty-cycle control on thin-SiO2 covered Si nanorod array is performed by O(2-) plasma pre-etching the self-assembled polystyrene nanosphere array mask with area density of 4 × 10(8) rod/cm(-2). The 120-nm high SiO2 covered Si nanorod array is obtained after subsequent CF4/O2 plasma etching for 160 sec. This results in a tunable nanorod diameter from 445 to 285 nm after etching from 30 to 80 sec, corresponding to a varying nanorod duty-cycle from 89% to 57%. The TM-mode reflection analysis shows a diminishing Brewster angle shifted from 71° to 54° with increasing nanorod duty-cycle from 57% to 89% at 532 nm. The greatly reduced small-angle reflectance reveals a nonlinear trend with enlarging duty-cycle, leading to a minimum surface reflectance at nanorod duty-cycle of 85%. Both the simulation and experiment indicate that such a surface reflectance minimum is even lower than that of a uniformly SiO2 covered Si substrate on account of its periodical nanorod array architecture with tuned duty-cycle.
authors.affiliation: Department of Electrical Engineering, Institute of Photonics and Optoelectronics, National Taiwan University, No. 1 Roosevelt Rd Sec 4, Taipei 10617, Taiwan.
authors.forename: Yi-Hao
authors.initials: YH
authors.lastname: Pai
authors.forename: Yu-Chan
authors.initials: YC
authors.lastname: Lin
authors.forename: Jai-Lin
authors.initials: JL
authors.lastname: Tsai
authors.forename: Gong-Ru
authors.initials: GR
authors.lastname: Lin
mesh_terms: D017076:Computer-Aided Design; D004867:Equipment Design; D019544:Equipment Failure Analysis; D036103:Nanotechnology / Q000295:instrumentation*; D043942:Nanotubes / Q000737:chemistry*; D017711:Nonlinear Dynamics; D010783:Photometry / Q000295:instrumentation*; D012666:Semiconductors